This invention relates to a method of preparing fibrous sheet materials wherein a fibre-pulp is treated in a defibrator so as to form a stream of gas containing suspended fibres, which stream of gas is caused to pass through a gas-permeable forming surface so as to form a fibrous layer thereon and wherein a binder is supplied to said fibrous layer to bond the fibres together.
It has been attempted to dye fibrous products prepared by methods of the above mentioned type by spraying onto the fibrous layers formed solutions of dyes or by impregnating such layers in a bath containing a dye solution. These methods of dyeing fibrous materials do not result in the formation of uniformly dyed products and when spraying a dye solution onto a fibrous product only the surface layers become dyed. This is unsatisfactory if the fibrous material subsequently is subjected to such influences that portions of the surface layers are abraded.
The object of the present invention is to obtain fibrous materials prepared by a dry process and in which all portions are uniformly dyed.